Computer systems may include performance profiling modules, which collect performance data pertaining to computer performance. For example, the performance profiling modules may monitor for one or more events. The performance data may be recorded in a suitable memory medium, e.g., a data file or a database, and may be analyzed by a performance analysis tool or presented to a user via a suitable user interface.
Some performance profiling modules collect performance data using sampling techniques, rather than continuous monitoring techniques. Performance profilers may associate two parameters for each event being monitored: an interval and an active fraction. The interval parameter records the number of events between samples. The active fraction parameter records how often the event was monitored. For example, events may be monitored for only a fraction of the time because more events were requested than hardware monitoring capabilities enable to be monitored, requiring some form of time-multiplexed sharing of the hardware resources.
Profiling modules may run monitoring sessions of varying time durations, and may monitor different sets of parameters during different monitoring sessions. In this event, the data sets collected must be merged in a manner that gives semantically meaningful presentations of the samples.